Tensile, solubility, and electrophoretic properties of egg white films as affected by surface sulfhydryl groups

Films plasticized with polyethylene glycol were cast from alkaline (pH 10.5, 11.0, or 11.5), aqueous egg white (EW) solutions with or without heating (40 degrees C for 30 min). Prior to casting, concentration of surface sulfhydryl (SH) groups was determined and they increased (P < 0.05) (3.81-19.45 mu M/g protein) with both pH and heating, presumably due to protein denaturation and cleavage of disulfide (S-S) bonds. Concentration of surface SH groups correlated (P < 0.05) with film tensile strength (r = 0.70), elongation at break (r = 0.86), and film total soluble matter (r = -0.94). Most likely, surface SH groups formed S-S bonds through air oxidation and/or sulfhydryl/disulfide interchange, thus contributing to EW film formation. SDS-PAGE patterns in presence or absence of 2-mercaptoethanol confirmed occurrence of S-S bonding in dried EW films.